Sunday, December 19, 2010

Zambia Agates

When I was exhibiting my mineral art at the East Grand Rapids art show, I was visited again by Shirley Schadle and her husband. Shirley grew up in Zambia where her father worked as a veterinarian. While there, she searched for agates in southern Zambia.

Since the Zambia agates look a lot like Lake Superior agates, I decided to do a little research to see if I could find out the geologic influences on agate formation in Zambia. Between 177 and 185 million years ago there were hot spots wherein molten material upwelled toward the surface of the earth. These plumes then erupted and spread basaltic lava over the surface of the earth. Geologists consider this a "large igneous province" when great quantities of basaltic lava spread over areas that are more than 38,610 square miles within a short period of geologic time.

It is interesting to note that this basaltic lava plume spread lava not only in Zambia, but also in Botswana and Zimbabwe. It is in the gas pockets of this basaltic lava that the agates formed.

Here is a map that approximates the basaltic lava fields.

This first specimen Shirley calls a Luangwa River Crab Agate. Although there may be some microcrystalline chalcedony, most of the quartz appears to be macrocrystalline.

The rest of the specimens that were kindly photographed by Shirley's husband clearly show agate structure. Notice how some of these look just like the specimens we find on our local Lake Superior beaches.

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